A general problem in the construction and use of many types of electronic apparatuses is the generation of input and control signals to the apparatus. In a typical electronic apparatus, and most particularly in portable, hand held electronic apparatuses, a keyboard is employed to make the electronic apparatus responsive to the user. Such keyboards typically include a plurality of momentary contact key switches. The electronic apparatus is constructed in order to be responsive to the closing of these momentary contact key switches, either along or in combination. Employing this technique it is possible for the operator to cause the electronic apparatus to perform the desired function.
A particularly advantageous manner for providing a keyboard for an electronic apparatus is the so called membrane keyboard. Such a membrane keyboard is low in cost and provides the advantage that it greatly reduces the number of holes necessary in the case of the electronic apparatus. This is advantageous for electronic apparatuses such as electronic learning aids or electronic games which are primarily used by children, because a membrane keyboard greatly reduces the risk of dirt or other foreign matter getting inside the case of the electronic apparatus.
The typical membrane keyboard includes a plurality of layers or separate sheets of a flexible material. Generally, a top sheet will have a plurality of row conductors imprinted thereon. A bottom sheet will have a plurality of column conductors imprinted thereon. A third sheet, which serves as both an insulator and a spacer is placed between the top and bottom sheets. This third sheet has a plurality of holes cut therein, each hole corresponding to a crossing position between a row conductor and a column conductor. In such a membrane keyboard, the row conductors and column conductors are normally held apart and prevented from making electrical contact by the insulating and spacing sheet. However, pressure applied to the top sheet at a position corresponding to an intersection between a row conductor and a column conductor, causes the top sheet to flex thereby bringing the row conductor and column conductor into electrical contact. This electrical contact is sensed as a switch closure by the electronic apparatus, thereby enabling the electronic apparatus to be responsive to the user. Release of the pressure on the top sheet causes the top sheet to return to its former position, thereby opening the electrical connection between the row conductor and the column conductor. However, the requirement for three separate sheets within this membrane keyboard makes the membrane keyboard more complicated and more expensive than could be achieved if one or more of these sheets could be eliminated.